During preparing a low temperature poly-silicon (LTPS) thin film transistor liquid crystal display (TFT-LCD), an excimer laser, used as a heat source, is projected onto an amorphous silicon structure prepared on a glass substrate. The amorphous silicon structure, after absorbing the energy of the excimer laser, is turned into a poly-silicon structure. Since the whole crystallization process is carried out below 600 centigrade, the process is referred to as low temperature process, and is suitable to most glass substrates.
The LTPS-TFT LCD is widely applied due to the advantages such as its high resolution, quick response, high brightness, high aperture ratio, and so on. However, in the conventional array substrate, it is necessary to use two mask plates to perform the photolithography process to form the gate electrode and the low doped region of a TFT, and therefore, after completing the gate electrode, the mask plate in the photolithography apparatus is changed to another one to form the low doped region. There may be some misalignment between the two mask plates and causing that the two low doped regions, which should be symmetrically located at the opposite sides of the gate electrode, has different length. Such low doped regions having different length reduces the ability of the TFT to suppress the leakage current, causes large leakage current, and thus increases the power consumption of the LTPS-TFT LCD.